Method of manufacturing a metallic layer on a non-metallic surface

ABSTRACT

A method of manufacturing a metallic layer on a non-metallic surface is disclosed. The method of manufacturing a metallic layer on a non-metallic surface includes the steps of: roughening the non-metallic surface; continuously feeding a first metallic wire and a second metallic wire above the non-metallic surface; positioning the first metallic wire and the second metallic wire so that the first metallic wire and the second metallic wire are in contact with each other at one end; applying a first voltage to the first metallic wire and applying a second voltage to the second metallic wire, wherein a voltage difference between the first voltage and the second voltage is large enough to produce an electric arc; melting the first and second metallic wire with the electric arc so as to form the metallic layer on the non-metallic surface; and forming a protection layer on the metallic layer to avoid the metallic layer from peeling off the non-metallic surface.

FIELD OF THE INVENTION

The present invention relates to a method of manufacturing a metallic layer, and more particularly, to a method of manufacturing a metallic layer on a non-metallic surface, e.g., a note-book personal computer case, or uses this technique to replace a metallic cover of a desktop computer.

BACKGROUND OF THE INVENTION

All electronic products emit electromagnetic radiation, generally in the range from 10 MHz to 3 GHz, but not limited to this range, especially considering the recent advances in high-speed microprocessor design and the rapidly increasing capabilities of high-speed networking and switching. The problem of emission of electromagnetic radiation is not new to designers of electronic equipment; indeed, significant efforts are taken to reduce electromagnetic interference, electrostatic discharge, radio frequency interference (hereinafter referred to collectively as “EMI”) and virtually every country has a regulating agency (FCC in the U.S., for instance) that restricts the marketing and sale of electronic equipment that do not pass stringent requirements for EMI, whether radiation or intercepted (also called susceptibility) by an electronic device.

Present day solutions for EMI shielding generally include the use of conductively painted plastic housings, conductive gaskets, and metal cans that are affixed to the printed circuit board by soldering or similar methods, some of which are semi-permanently attached to the printed circuit board. In virtually all cases, however, the existing solutions are expensive and add significant costs to providing electronic equipment such as cellular phones, personal digital assistants (PDA), laptop computers, set-top boxes, cable modems, networking equipment including switches, bridges, and cross-connects, among a multitude of other electronic products.

In an effort to bring cost down while increasing EMI shielding, various technologies utilizing metallic polymer substrates have been developed for use as an effective EMI shielding solution. For example, U.S. Pat. No. 5,811,050 to Gabower, the complete disclosure of which is incorporated herein by reference, has provided a shielding approach wherein a thermoformable substrate (any number of polymers) is first thermoformed and then metallized. This approach offers the advantage of eliminating any stresses that may occur during thermoforming to a metallic layer that is applied to the substrate prior to the forming process. The product has been shown to be a highly effective and a relatively low-cost method for providing effective EMI control (also called electromagnetic compatibility or EMC) for electronic products.

Utilizing formed plastic shields that have been metallized has proven to be an effective shielding method that reduces the cost and overall weight associated with shielding of an electronic device.

Plating and electroplating are commonly used in the coating industry to apply a metallic coating, such as chromium, to a metallic or plastic substrate. The metallic coating is often composed of multiple metal layers plated directly on top of each other, typically copper and nickel before a final layer of chromium.

For both metallic and plastic substrates, a smooth surface is desirable to carry out an electroplating operation to deposit the metal layer(s). For metal substrates, it is often required to perform several surface preparation steps, including sanding, buffing and polishing, to remove any pits, scratches, or porosity from the surface. If these surface defects are not removed, they may be clearly noticeable in the final product. Likewise, certain ceramics may present a porous surface that cannot be plated or coated without significant surface preparation and/or sealing. In the case of porous substrates such as metal castings or extrusions, thick layers of zinc and copper usually are plated on the substrate to seal the porous surface, then physically polished before the final decorative metal layer can be plated to the surface. These operations present burdens of increased production time, manpower, materials and energy, as well as environmental costs.

Liquid paint compositions also can be used to provide a particular aesthetic appearance, such as a metallic chrome-like appearance. Incorporating metal flake pigments into the paints can provide a simulated plated appearance. These flakes must nearly touch or slightly overlap each other as a stratified layer within the paint film to simulate the look of a contiguous film. As the concentration and film density of metallic pigments are increased, it becomes more difficult to uniformly coat the metal flakes, thereby weakening the internal cohesive properties of the paint film. Highly loaded metallic paint films are susceptible to intra-coat adhesion failure causing poor environmental durability.

Thermoset paint requires the application of heat to create the cross-linking and cure necessary within the paint to produce a desired appearance. In an attempt to increase the crosslink density of the final paint film, a process of increasing either or both temperature and time during the cure bake is used to increase the extent of cure. While for some formulations this process can increase the crosslink density of the final paint film, it is generally regarded as undesirable because exposing the paint film to temperatures and durations exceeding those recommended by the manufacturer degrades the polymeric vehicle of the paint system. Overbaking the polymeric vehicle can result in loss of gloss, embrittlement, loss of adhesion, and reduced environmental durability. In addition, a significant number of substrates, such as certain types of aluminum or steel castings, are heat tempered and cannot be reheated beyond 400° F. without compromising the structural integrity of the substrate.

It is also known to apply a nickel-chrome alloy and chrome coating by vacuum metallization onto a metal substrate thereby eliminating the application of the decorative metal coating utilizing hazardous solutions. This process entails first applying a polymeric thermosetting powder as a primer coat to provide a smooth surface for the decorative metal coatings. The primer coat is cured at temperatures at or above 450° F. for up to 90 minutes to provide a suitable adhesion surface for the nickel-chrome alloy and chrome metal layers. Subsequent to curing the primer coat, the respective nickel-chrome and chrome metal layers are applied in separate vacuum deposition steps. Upon metallization, the part can be further coated with a different thermosetting powder at a temperature at or above 320° F. for a period of 25 minutes or longer. However, any surface imperfections on the surface of the primer coat will be highlighted in the decorative metal layer deposited thereon.

The process described above has several disadvantages. First, the utilization of high heat for a long duration during the initial primer coat step can change the temper of the metal substrate. Second, -two metal layers are applied by separate and successive vacuum deposition steps. These separate steps extend the deposition time beyond a single layer process and cause a decrease in production efficiency. Third, different coating metals for deposition may require different vapor pressures for proper deposition. Different vapor pressures may require additional pumping time, consuming additional production time. Also, using different thermosetting materials can present contamination problems in the application of each material. Finally, it is common in the paint industry that cross contamination of epoxy and acrylic powders is a potential source for surface defects, such as craters and pin-holing. Parts exhibiting such defects after coating are usually not acceptable to the end-user and require the producer to either strip the part prior to reprocess or scrap the part. Therefore, a method of manufacturing a metallic layer on a non-metallic surface with low production cost and short production time is highly desired.

SUMMARY OF THE INVENTION

This paragraph extracts and compiles some features of the present invention; other features will be disclosed in the follow-up paragraph. It is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, and this paragraph also is considered to refer.

In accordance with an aspect of the present invention, a method of manufacturing a metallic layer on a non-metallic surface includes the steps of: roughening the non-metallic surface; continuously feeding a first metallic wire and a second metallic wire above the non-metallic surface; positioning the first metallic wire and the second metallic wire so that the first metallic wire and the second metallic wire are in contact with each other at one end; applying a first voltage to the first metallic wire and applying a second voltage to the second metallic wire, wherein a voltage difference between the first voltage and the second voltage is large enough to produce an electric arc; melting the first and second metallic wire with the electric arc so as to form the metallic layer on the non-metallic surface; and forming a protection layer on the metallic layer to avoid the metallic layer from peeling off the non-metallic surface.

Preferably, the first and second metallic wires form a metallic coating after being melted.

Preferably, further includes a step of atomizing the metallic coating material.

Preferably, the atomizing step is achieved by blowing a gas flow to the metallic coating material.

Preferably, the gas flow has a pressure of approximately 3˜20 bar.

Preferably, the gas flow is compressed air or inert gas.

Preferably, further includes a step of spreading the atomized metallic coating material onto the non-metallic surface to form the metallic layer.

Preferably, further includes a step of roughening the non-metallic surface before the spreading step.

Preferably, the non-metallic surface has a roughness larger than 4 nanometers after the roughening step.

Preferably, further includes a step of hardening the metallic coating material on the non-metallic surface.

Preferably, the voltage difference is approximately between 10˜40 volts.

Preferably, the non-metallic surface has a temperature range from 5° C. to 90° C. after the atomized metallic coating material is being spread onto the non-metallic surface.

Preferably, the first metallic wire and the second metallic wire each has a diameter of approximately 0.5˜2.5 mm.

Preferably, a current of 70˜350 A is generated between the first metallic wire and the second metallic wire while continuously feeding the first and second metallic wires and applying the first and second voltages on the first and second metallic wires.

Preferably, the first metallic wire and the second metallic wire are made of an identical material.

Preferably, the first metallic wire and the second metallic wire are made of different materials.

Preferably, the first metallic wire and the second metallic wire includes Zn, Pb, Al, Cu, Mg, Zr, Ag, Ti, Fe, Be, Au, or an alloy thereof.

Preferably, the protection layer includes polyvinyl butyral resin, poly-urethane, polyester resin, vinyl-ester resin, unsaturated poly vinyl-ester resin, epoxy resin, or ultra-violet curing paint.

Preferably, the protection layer is formed by sputtering.

Preferably, the protection layer includes Zn, Cr, Ni, Ti, Zr, or stainless steel (including 200, 300, 400, 500, 600 Series).

Preferably, the metallic layer has a thickness of approximately 0.5˜3000 μm on substrate exterior surface and/or 0.5˜25 μm on substrate interior surface.

Preferably, the metallic layer has a roughness of approximately 0.4˜500 μm.

Preferably, the non-metallic surface includes polyethylene (PE), polyimide (PI), polyamide (PA), acrylonitrile-butadiene-styrene (ABS), polycarbonate (PC), polyvinyl chloride (PVC), polyphenylene ether (PPE), polystyrene (PS), polyetherimide (PEI), polybutylene terephathalate (PBT), polyethylene terephathalate (PET), acrylic resin (PMMA), polymethacrylate (PMA), polyurethane (PU), polyolefin, polysulfone (PSF), liquid crystalline polymer (LCP), polyarylate (PAR), polyether ether ketone (PEEK), polytetrafluorcethylene (PTFE), polyoxybenzylene (POB), polyphenylene sulphide (PPS), polyphenylene oxide (PPO), Polyphthalamide (PPA), polyoxy methylene (POM), polyphenylene sulfide (PES), carbon fiber, glass fiber, boron fiber or paper.

BRIEF DESCRIPTION OF THE DRAWING

The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which:

FIG. 1 illustrates a schematic diagram of a metallic layer on a non-metallic surface according to the present invention;

FIG. 2 illustrates a schematic diagram of a method of manufacturing a metallic layer according to the present invention; and

FIG. 3 illustrates a flow chart of a method of manufacturing a metallic layer according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will now be described more specifically with reference to the following embodiment. It is to be noted that the following description of preferred embodiment of this invention is presented herein for purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed.

With reference to FIG. 1 and FIG. 2, this embodiment provides a method to coat a metallic layer 100 onto a surface 12 of a non-metallic substrate 10. The substrate 10 can be a housing of a cellular phone, personal digital assistant (PDA) or laptop computer.

As shown at step S301 and S302 of FIG. 3, the embodiment needs to continuously provide a first metallic wire 102 and a second metallic wire 104 and to have them be placed properly mentioned in the following paragraph. The material of the first metallic wire 102 and of the second metallic wire 104 can be identical. However, depending on different requirements of products, the first metallic wire 102 can differ from the second metallic wire 104 in material. The materials of the first metallic wire 102 and of the second metallic wire 104 can be Zn, Pb, Al, Cu, Mg, Zr, Ti, Ag, Fe, Be, Au, an alloy thereof, the combination of these metallic materials or other proper metallic materials. A diameter between 0.6 mm and 2.0 mm is preferred for the first metallic wire 102 and the second metallic wire 104.

The first metallic wire 102 can be placed inside one conveyance duct 202 a, and the second metallic wire 104 can be placed inside the other conveyance duct 202 b, as shown in FIG. 2. The first metallic wire 102 can be transported into the conveyance duct 202 a by a pair of conveyance rollers 204 a, and the second metallic wire 104 can be transported into the conveyance duct 202 b by a pair of conveyance rollers 204 b. Then, a first voltage V1 and a second voltage V2 are applied to the first metallic wire 102 and the second metallic wire 104 respectively, as shown at step S303 of FIG. 3. The first voltage V1 can be directly applied on the conveyance duct 202 a, and further conducted to the first metallic wire 102 indirectly. The second voltage V2 can be directly applied on the conveyance duct 202 b, and further conducted to the second metallic wire 104 indirectly. Due to the voltage difference between the first voltage V1 and the second voltage V2, which is more than 10V, and the contact of the first metallic wire 102 with the second metallic wire 104, an electric arc is induced in an electric arc area R between the first metallic wire 102 and the second metallic 104 wire at the contact end. The voltage difference between the first voltage V1 and the second voltage V2 should be less than 40V. 25V is recommended. An electric current between the first metallic wire 102 and the second metallic wire 104 ranges from 70 A to 350 A when continuously feeding the first metallic wire 102 and the second metallic wire 104 and applying the first voltage V1 and the second voltage V2 on the first metallic wire 102 and the second metallic wire 104. With the electric arc, a portion of the first metallic wire and a portion of the second metallic wire will be heated to melt or vaporize in the electric arc area R, further forming a melted metallic coating material 106, as shown at steps S304 and S305 of FIG. 3. The melted metallic coating material 106 can include one or more metallic materials

Before the melted metallic coating material 106 is spread onto the surface 12 of the non-metallic substrate 10, the surface 12 of non-metallic substrate 10 should be cleaned and roughened, as shown at step S306 of FIG. 3. The roughness of the surface 12 will become more than 4 nanometers after roughening. Therefore, the adhesion of the melted metallic coating material 106 to surface 12 of non-metallic substrate 10 will increase as well. If the surface 12 of non-metallic substrate 10 is already clean and rough enough, it is not necessary to perform cleaning and roughening on the surface 12 of non-metallic substrate 10.

Next, the melted metallic coating material 106 will be atomized by a blowing gas G shown at step S307 of FIG. 3. The blowing gas G can be compressed air or inert gas, sprinkled out of a nozzle 206 with a pressure from 3 bar to 20 bar, e.g., 6 bar. The blowing gas G brings the atomized melted metallic coating material 106 toward the surface 12 of non-metallic substrate 10, as shown at step S308 of FIG. 3. Therefore, the melted metallic coating material 106 is able to adhere onto the surface 12 of non-metallic substrate 10.

The surface temperature of the non-metallic substrate 10 increases while in contact with the melted metallic coating material 106 which may cause distortion of the non-metallic substrate 10. Therefore, compressed air or inert gas is used to lower the surface temperature of the non-metallic substrate 10. Furthermore, higher pressure can be added to reduce the surface temperature of the non-metallic substrate 10, too.

The substrate 10 can be made of plastics, paper, cloth, rubber and timber. Furthermore, the substrate 10 can be made of materials such as polyethylene (PE), polyimide (PI), polyamide (PA), acrylonitrile-butadiene-styrene (ABS), polycarbonate (PC), polyvinyl chloride (PVC), polyphenylene ether (PPE), polystyrene (PS), polyetherimide (PEI), polybutylene terephathalate (PBT), polyethylene terephathalate (PET), acrylic resin (PMMA), polymethacrylate (PMA), polyurethane (PU), polyolefin, polysulfone (PSF), liquid crystalline polymer (LCP), polyarylate (PAR), polyether ether ketone (PEEK), polytetrafluorcethylene (PTFE), polyoxybenzylene (POB), polyphenylene sulphide (PPS), polyphenylene oxide (PPO), Polyphthalamide (PPA), polyoxy methylene (POM), polyphenylene sulfide (PES), carbon fiber, glass fiber, boron fiber, and so on.

In the process of step S308, the temperature of melted metallic coating material 106 contacting the surface 12 of non-metallic substrate 10 ranges from 5° C. to 90° C. Since the temperature is not high so that it is acceptable to spread onto the substrate 10 mentioned above. The melted metallic coating material 106 on the surface 12 of non-metallic substrate 10 will not cause the substrate 10 to be softened or deformed.

Since the temperature when the melted metallic coating material 106 contacts the surface 12 of non-metallic substrate 10 ranges from 5° C. to 90° C., the melted metallic coating material 106 on the surface 12 of non-metallic substrate 10 will soon drop its temperature down to lower than the melting point. After adhering to the surface 12 of non-metallic substrate 10, the melted metallic coating material 106 becomes hardened by cooling. The metallic coating material 106 forms the metallic layer 100. It is shown at step S309 of FIG. 3. Besides, adjustment of pressure applied to blowing gas G controls the flow speed of blowing gas G to the surface 12 of the non-metallic substrate 10, thereby controlling the temperature when the melted metallic coating material 106 contacts the surface 12 of non-metallic substrate 10. For more details, the larger pressure of the blowing gas G is applied, the lower temperature when the melted metallic coating material 106 contacts the surface 12 of non-metallic substrate 10 will be, and the smaller pressure of the blowing gas G is applied, the higher temperature when the melted metallic coating material 106 contacts the surface 12 of non-metallic substrate 10 will be.

Since the materials of the first metallic wire 102 and of the second metallic wire 104 can be identical or different, the metallic layer 100 is made of a single metal or alloy which comprises many kinds of metals.

It deserves to be mentioned that the larger voltage difference between the first voltage V1 and the second voltage V2 is, the more electric current is induced between the first metallic wire 102 and the second metallic wire 104, and thus there will be more melted metallic coating material 106 produced. Therefore, when the voltage difference between the first voltage V1 and the second voltage V2 gets larger, thicker metallic wire can be used for the first metallic wire 102 and the second metallic wire 104. With more melted metallic coating material 106, the plating rate increases. The rate of forming the metallic layer 100 becomes fast as well, further reducing the time to form the metallic layer 100.

Referring back to FIG. 1, the metallic layer 100 made by the method mentioned in the embodiment usually contains many pores. It is needed to form a protection layer 108, as shown at step S310 of FIG. 3, to cover the metallic layer 100 and seal these pores. Furthermore, the protection layer 108 is used to avoid the metallic layer 100 from peeling off the non-metallic substrate 10. In this embodiment, a resin material with good fluidity can be used for the protection layer 108. For instance, material of the protection layer 108 can be polyvinyl butyral resin, poly-urethane, polyester resin, vinyl-ester resin, unsaturated poly vinyl-ester resin, epoxy resin, ultra-violet curing paint, or any combination of these materials. Furthermore, in order to enhance the shielding effect, an extra shielding material (normally in powder form) can be added and mixed into the resin before applied to the metallic layer 100, such a material including C, Zn, Pb, Al, Cu, Mg, Zr, Ti, Fe, Be, Ag, Au, or an alloy thereof. The protection layer 108 can also be formed by sputtering while the protection layer 108 is made of Zn, Cr, Ni, Ti, Zr, stainless steel (including 200, 300, 400, 500, 600 Series), or an alloy thereof.

To summarize all descriptions mentioned above, the invention is able to provide a metallic layer on a housing of an electronic device by spreading the melted metallic coating material. Therefore, the housing of the electronic device can shield EMI, further reducing the influence of EMI on health of human-being.

Besides, compared with prior art sputtering and vapor deposition, since the invention doesn't need to use vacuum chamber or vacuum pump on the shielding layer, producing a metallic layer costs less.

Furthermore, since the voltage difference between the first voltage and the second voltage is more than 10V, there will be plenty of melted metallic coating material formed with the use of this invention. The rate of plating of metallic coating material increases while the time to make the metallic layer reduces effectively.

Finally, it needs not to perform the inventive method in a vacuum environment, and the melted metallic coating material spread on a housing of an electronic device can be hardened very soon due to low temperature when melting. The invention has another advantage to shorten the time for making a metallic layer.

While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, which are accorded with the broadest interpretation so as to encompass all such modifications and similar structures. 

1. A method of manufacturing a metallic layer on a non-metallic surface, comprising the steps of: roughening said non-metallic surface; continuously feeding a first metallic wire and a second metallic wire above said non-metallic surface; positioning said first metallic wire and said second metallic wire so that said first metallic wire and said second metallic wire are in contact with each other at one end; applying a first voltage to said first metallic wire and applying a second voltage to said second metallic wire, wherein a voltage difference between the first voltage and the second voltage is large enough to produce an electric arc; melting said first and second metallic wire with said electric arc so as to form said metallic layer on said non-metallic surface; and forming a protection layer on said metallic layer to avoid said metallic layer from peeling off said non-metallic surface.
 2. The method according to claim 1, wherein said first and second metallic wire form a metallic coating material after being melted.
 3. The method according to claim 2, further comprising a step of atomizing said metallic coating material.
 4. The method according to claim 3, wherein said atomizing step is achieved by blowing a gas flow to said metallic coating material.
 5. The method according to claim 4, wherein said gas flow has a pressure of approximately 3˜20 bar.
 6. The method according to claim 4, wherein said gas flow is compressed air or inert gas.
 7. The method according to claim 3, further comprising a step of spreading said atomized metallic coating material onto said non-metallic surface to form said metallic layer.
 8. The method according to claim 1, wherein said non-metallic surface has a roughness larger than 4 nanometers after the roughening step.
 9. The method according to claim 7, further comprising a step of hardening said metallic coating material on said non-metallic surface.
 10. The method according to claim 1, wherein said voltage difference is approximately between 10˜40 volts.
 11. The method according to claim 7, wherein said non-metallic surface has a temperature range from 5° C. to 90° C. after said atomized metallic coating material is being spread onto said non-metallic surface.
 12. The method according to claim 1, wherein said first metallic wire and said second metallic wire each has a diameter of approximately 0.5˜2.5 mm.
 13. The method according to claim 1, wherein a current of 70˜350 A is generated between said first metallic wire and said second metallic wire while continuously feeding said first and second metallic wires and applying said first and second voltages on said first and second metallic wires.
 14. The method according to claim 1, wherein said first metallic wire and said second metallic wire are made of an identical material.
 15. The method according to claim 1, wherein said first metallic wire and said second metallic wire are made of different materials.
 16. The method according to claim 1, wherein said first metallic wire and said second metallic wire comprises Zn, Pb, Al, Cu, Mn, Zr, Ti, Ag, Fe, Be, Au, or an alloy thereof.
 17. The method according to claim 1, wherein said protection layer comprises polyvinyl butyral resin, poly-urethane, polyester resin, vinyl-ester resin, unsaturated poly vinyl-ester resin, epoxy resin, or ultra-violet curing paint.
 18. The method according to claim 17, wherein said protection layer further comprises C, Zn, Pb, Al, Cu, Mg, Zr, Ti, Fe, Be, Ag, Au, or an alloy thereof.
 19. The method according to claim 1, wherein said protection layer is formed by sputtering.
 20. The method according to claim 19, wherein said protection layer comprises Zn, Cr, Ni, Ti, Zr, or stainless steel.
 21. The method according to claim 1, wherein said metallic layer has a thickness of approximately 0.5˜3000 μm on substrate exterior surface or 0.5˜25 μm on substrate interior surface.
 22. The method according to claim 1, wherein said metallic layer has a roughness of approximately 0.4˜500 μm.
 23. The method according to claim 1, wherein said non-metallic surface comprises polyethylene (PE), polyimide (PI), polyamide (PA), acrylonitrile-butadiene-styrene (ABS), polycarbonate (PC), polyvinyl chloride (PVC), polyphenylene ether (PPE), polystyrene (PS), polyetherimide (PEI), polybutylene terephathalate (PBT), polyethylene terephathalate (PET), acrylic resin (PMMA), polymethacrylate (PMA), polyurethane (PU), polyolefin, polysulfone (PSF), liquid crystalline polymer (LCP), polyarylate (PAR), polyether ether ketone (PEEK), polytetrafluorcethylene (PTFE), polyoxybenzylene (POB), polyphenylene sulphide (PPS), polyphenylene oxide (PPO), Polyphthalamide (PPA), polyoxy methylene (POM), polyphenylene sulfide (PES), carbon fiber, glass fiber, boron fiber, or paper. 